DALLAS—Toll roads are experiencing a growth spurt around the U.S. as states strapped for cash look to relieve traffic congestion without raising taxes.

But a political backlash is rising in Texas, one of the states that most aggressively encouraged toll-road construction, as residents realize that many major urban freeways are increasingly no longer free.

Here in the Dallas-Fort Worth area, the fourth-largest metropolitan region in the U.S., with more than 6.5 million people, public and private entities have constructed one of the most extensive toll-road networks in North America—and numerous additional toll roads are on the horizon.

Transportation officials are considering converting part of U.S. Highway 75, a major north-south artery, to toll lanes. And Texas Turnpike Corp., a private company that possesses eminent-domain powers under a since-revised law, is proposing to build a highway northeast of Dallas that would be one of the only fully privately built, owned and operated toll roads in the country.

“It’s almost impossible to get around without paying a toll now,” said Bobby Tillman, a 63-year-old web developer from Sachse, Texas, who spoke against the road at a public hearing last month that filled a 1,500-seat high-school auditorium. “We pay taxes for roads and bridges, and if that’s not enough, if you can’t afford it, don’t build it.”

The toll boom is taking place in part because a primary source of highway-construction funding in the U.S., a federal tax of 18.4 cents per gallon on gasoline, hasn’t changed since 1993. Many states also haven’t raised state gasoline taxes for decades, including Texas, which hasn’t increased its 20-cents- per-gallon tax since 1991.

While still a fraction of freeways, toll roads make up a growing percentage of newly built and upgraded roads in certain regions of the country. More than 5,400 miles of U.S. roads now require tolls, up 15% from a decade earlier, according to a 2013 report by the Federal Highway Administration. The Obama administration in April proposed allowing states to collect tolls on interstate highways, most of which are currently free. But the idea has run into bipartisan opposition in Congress.

Texas has more than 500 miles of toll roads, the majority of which were constructed in the past 10 years, according to the Texas Department of Transportation. An additional two dozen toll-road projects are in the planning or construction stages, which could add more than 300 additional tolled miles in the state, according to the agency.

Other states, such as Florida, have likewise facilitated toll-road building in recent years. “The number of toll roads in Florida has increased to meet the demands of a growing population,” said a spokeswoman with Florida’s Turnpike Enterprise, a unit of the state’s department of transportation.

Miami resident Carlos Garcia, the co-founder of RollBackTolls.com, said in certain parts of the state, particularly Miami and Orlando, it increasingly feels like there are few free alternatives to toll roads.

“Many people in Florida believe we face double taxation: first the gas tax and, second, tolls,” he said.

In Texas, lawmakers have embraced public-private partnerships in which a private party helps finance the construction of new tolled highways or the tolling of existing highways in exchange for receiving a share of future revenue.

“What makes more sense, raising gas taxes to build roads or giving drivers the option to pay service fees?” said Robert Nichols, the Republican chairman of the Texas Senate’s transportation committee.

Even with toll roads, Texas, the nation’s second-largest state, with more than 26 million people, faces a transportation-funding gap of $5 billion a year as it seeks to limit congestion to 2010 levels, according to David Ellis, a research scientist at the Texas A&M Transportation Institute. A November ballot measure, which polling suggests is likely to pass, would let the state shift more than $1 billion a year from its rainy-day fund to its highway fund, but road experts say it wouldn’t entirely resolve the problem.

“There is not a road fairy, and you have to find some way to build these roads,” Mr. Ellis said in an interview.

However, Texas toll roads face mounting opposition, including within the state’s Republican Party, which amended its platform this year to add language hostile to toll roads. “A large segment of our party believes in having free access to transportation,” said Steve Munisteri, chairman of the Republican Party of Texas.

Texas lawmakers are reacting to criticism in areas such as Collin County, north of Dallas. There, the proposal to convert lanes on U.S. Highway 75 to tolls sparked a firestorm from residents who noted that Plano, Texas, would be nearly surrounded by toll roads.

“I like to say we are a gated community,” said Republican state Rep. Jeff Leach, adding that toll roads are “way up there” among issues his conservative constituents are worked up about.

Still, while toll-road proponents acknowledge changing political realities, they predict Texas and other states will continue adding toll lanes.

“The truth is that most people are using and liking these toll roads,” said John Crew, the majority owner of Texas Turnpike Corp., the entity looking to build the private road near Dallas. “If we don’t build these things, it’s not going to be pretty in a few decades.”